Recently, in order to connect a video output apparatus such as a digital camera to a video display apparatus such as a monitor, it is general to use an HDMI (High-Definition Multimedia Interface) that is an interface for video data transmission.
In an HDMI, information is transmitted between connected devices mainly using a TMDS (Transition Minimized Differential Signaling) channel, a CEC (Consumer Electronics Control) channel, and a DDC (Display Data Channel).
The TMDS channel is a signal line that transmits video data, audio data, and auxiliary data. Further, the CEC channel is a signal line that transmits a device control signal. The use of communication using CEC commands (hereinafter referred to as CEC communication) enables a video display apparatus and an image capture apparatus to mutually acquire device information or one of them to control the other and vice versa.
The DDC is a signal line that transmits EDID (Extended Display Identification Data) (communication using a DDC is hereinafter referred to as DDC communication).
The EDID contains, in addition to display performance information such as resolution information indicating the display capabilities of the video display apparatus and audio output performance, physical address information for identifying a physical connection position of a connected device. Besides, the HDMI also has an HPD line used for the transmission of an HPD (Hot Plug Detect) signal described below, and a 5VPower line for supplying 5V power (hereinafter referred to as 5VPower) from the video data output side to the video data receiving side.
A video display apparatus connected to a video output apparatus via an HDMI determines, upon receipt of a 5VPower input from the video output apparatus, that a video data input request and a DDC communication access request have been issued, and switches the HPD (Hot Plug Detect) signal from an OFF level to an ON level. The video output apparatus detects that the HPD signal has been changed to the ON level via the HPD line, and newly starts DDC communication. Conversely, when the 5VPower supply is stopped in a state where the video output apparatus and the video display apparatus are electrically connected to each other, the HPD signal is switched from the ON level to the OFF level, and the electrical connection is disconnected.
In the DDC communication, the video output apparatus initially executes the process of acquiring EDID from the video display apparatus. When the EDID of the video display apparatus has been successfully acquired by the execution of the above process, the video output apparatus outputs video data to the video display apparatus.
Japanese Patent Laid-Open No. 2007-78980 describes a technique concerning DDC communication of an HDMI. In this technique, if video data transmitted from the transmitting device side has a different format from that set on the receiving device side, the receiving device once changes the HPD signal to the OFF level and then to the ON level, thereby once initializing the HDMI connection and executing new DDC communication. That is, this technique is used to forcibly disconnect an electrical connection by changing the HPD signal to the OFF level, and to allow the transmitting device to acquire EDID again to establish an electrical connection by changing the HPD signal again to the ON level.
Subsequently, as a preferred example in which a problem to be solved by the claimed invention occurs, a video processing system including a digital camera having a live view function and a video display apparatus connected to the digital camera using an HDMI will be described.
Recent single-lens reflex type digital cameras have a function called a live view function. The live view function is a function for capturing incident light transmitted through a lens using an image pickup element, converting the light into preview video data, and displaying the video data on a display device such as a liquid crystal screen of a digital camera in real time. A digital camera having the live view function allows a photographer to perform focus adjustment or photography while checking a live view image displayed on the display device instead of using a viewfinder. Therefore, the use of the live view function enables the confirmation of focus or composition before shooting still images even in photography performed at an angle at which the viewfinder is difficult to see.
Furthermore, a digital single-lens reflex camera having the live view function supports HDMI connections, thus allowing the digital camera to be connected to a video display apparatus such as a monitor so that live view video can be displayed on the screen of the monitor before being taken. The use of the above shooting method enables photography with confirmation of focus or composition using a large monitor instead of using a small liquid crystal screen of a digital camera, which is very convenient.
In a live view shooting mode in which photography is performed using live view video, however, a digital camera may temporarily stop video output, and, in some cases, the 5VPower supply of the HDMI may be stopped along with the stop of video output. Here, the configuration of a digital camera will be briefly described in order to describe the reason why video output is temporarily stopped in the live view shooting mode.
FIG. 9 is a configuration diagram illustrating a schematic configuration of a single-lens reflex type digital camera. A digital single-lens reflex camera 1000 serving as a video output apparatus includes, in the preceding stage of an image pickup element 1001, a movable mirror (reflector) 1002 that can advance and retract with respect to a photographic optical path by using a mirror drive unit 1007. In a normal time, the movable mirror 1002 is located at a position that is in the photographic optical path, and guides incident light transmitted through an image capture lens 1003 to a viewfinder 1004. The movable mirror 1002 is configured to, thereafter, immediately before photography, retract from the photographic optical path. Depending on whether or not the movable mirror 1002 is located at the position that is in the photographic optical path, the element to which the incident light is guided is alternately switched between the viewfinder 1004 and the image pickup element 1001. Further, the movable mirror 1002 includes a half mirror around the center thereof, and a sub-mirror 1006 for guiding object light transmitted through the half mirror to a focus control sensor 1005 is provided on a rear surface of this movable mirror. When the movable mirror 1002 retracts from the photographic optical path, the sub-mirror 1006 retracts in association therewith. When the movable mirror 1002 is in the photographic optical path, as described above, the sub-mirror 1006 is located at a position that is open with respect to the movable mirror 1002 in order to guide the object light to the focus control sensor 1005.
In the live view shooting mode, meanwhile, a CPU 1011 of the digital single-lens reflex camera 1000 brings the movable mirror 1002 into a retraction state at a normal time so that a video data output unit 1008 converts object light captured by the image pickup element 1001 into video data. When the converted video data is not output to the outside of the camera, video generated from the video data is displayed on a display device (not illustrated) provided in the digital single-lens reflex camera 1000.
Further, when the video data is output to a video display apparatus connected via an HDMI, the CPU 1011 performs control to output the video data from an HDMI terminal 1010 as a TMDS data signal through an HDMI transmitter 1009.
Here, when a user presses a shutter button (not illustrated) in a state where video data is being output to the video display apparatus, that is, in a state where the movable mirror 1002 is caused to retract from the photographic optical path, the CPU 1011 controls the movable mirror 1002 to once enter the photographic optical path from the retraction state to perform focus control and then to be in the retraction state again. Consequently, the object light to be input to the image pickup element 1001 is temporarily interrupted, and the input of the video data to the video data output unit 1008 is also temporarily interrupted. Accordingly, no video data is input from the video data output unit 1008, and in some cases, the HDMI transmitter 1009 may execute control to stop the 5VPower supply to the video display apparatus. Thus, the video display apparatus recognizes that the HDMI connection has been stopped (disconnected), and changes the HPD signal from an ON level to an OFF level. Consequently, the electrical connection between the video display apparatus and the digital single-lens reflex camera 1000 is disconnected.
Thereafter, when the movable mirror 1002 is in the retraction state again, the input of the object light to the image pickup element 1001 and the input of an electrical signal to the video data output unit 1008 are restarted. Accordingly, the video data output unit 1008 again outputs video data to the HDMI transmitter 1009. Upon receipt of the input of the video data, the HDMI transmitter 1009 changes the 5VPower output to the ON level again using the input of the video data as a trigger, and provides 5VPower supply to the video display apparatus using a 5VPower line.
Upon detection of the occurrence of a 5VPower input, the video display apparatus determines that a video data input request and a DDC communication access request have been issued, and starts control for changing the HPD signal from the OFF level to the ON level.
In this manner, many battery-driven apparatuses such as digital cameras stop 5VPower supply when no video data is input to an HDMI transmitter from the video data output unit 1008. This is presumably because, due to the increase in power consumption which is caused by supply of power to an external apparatus even when no video data is output to the external apparatus, the reduction in driving time of the apparatuses is prevented.
As described above, on the video output apparatus side, 5VPower supply to a video display apparatus is provided at the time when new video data is input to a transmitter that outputs video data, and, conversely, if no video data is input to the transmitter, the 5VPower supply is stopped. On the video display apparatus side, the presence of a 5VPower input is associated with the state transition of the HPD signal. Thus, if no video data is input to the transmitter on the video output apparatus side, the video display apparatus automatically disconnects the electrical connection with the video output apparatus. This is a significant operation when power is turned off on the video output apparatus side or at the time of the transition of the video output apparatus from the live view shooting mode to the normal shooting mode. However, if, as in during photography in the live view shooting mode, the input of video data to the HDMI transmitter 1009 is temporarily stopped and immediately thereafter video data is re-input, it is not desirable that the electrical connection be disconnected.
The reason that it is not desirable that the connection be disconnected is to require much time to re-establish an HDMI connection. During the HDMI connection, in response to the occurrence of a 5VPower input, the video display apparatus turns the HPD signal to an ON level. On the video output apparatus side where the above state has been recognized, a request for acquiring EDID is issued using DDC communication, and the process for receiving the EDID sent from the video display apparatus is executed. The above series of processes requires much time. Consequently, on the video display apparatus side, no video is displayed for a long period of time from when photography is executed to when the video display apparatus acquires the EDID and restarts video output.
For example, a digital single-lens reflex camera, which is manufactured by CANON KABUSHIKI KAISHA (under the name of EOS7D in Japan), and a liquid crystal television, which is manufactured by Toshiba Corporation (under the name of REGZA Z3500 in Japan), are connected using an HDMI cable, and the camera is set to the live view shooting mode. With the setting to this mode, the HDMI electrical connection process described above is performed, and finally live view video is displayed on a display screen of the television. When a shutter button of the camera is pressed in this state, the image displayed on the screen of the television disappears and about ten seconds are required until live view video output from the camera is displayed again, which has been found through the examination of the applicant. Similar problems also occur when an HDMI connection is set up between the digital single-lens reflex camera above, which is manufactured by CANON KABUSHIKI KAISHA, and a liquid crystal television, which is manufactured by Sony Corporation (under the name of KDL-40F1 in Japan), which has been confirmed by the applicant.
About ten seconds are required after photography in the live view shooting mode until live view video is displayed again on a video output apparatus because of, needless to say, the occurrence of electrical disconnection and connection processes for an HDMI connection. A live view video non-display period of about ten seconds can significantly reduce the efficiency of live view shooting, resulting in impairment of user convenience.
Japanese Patent Laid-Open No. 2007-78980 does not provide any consideration for the above problems concerning the change in the state of 5VPower supply that is caused by the stop and re-input of video data to the HDMI transmitter and the disconnection and connection processes for an HDMI connection which occur in correspondence therewith. Consequently, the technique disclosed in Japanese Patent Laid-Open No. 2007-78980 cannot solve the above problems.
It is to be understood that the above problems are not specific only to HDMIs. Similarly to HDMIs, any communication means that disconnects an electrical connection when the supply of power from a video output apparatus is interrupted may experience the above problems. Furthermore, not only digital cameras having the live view function but also apparatuses that output video to an external apparatus using communication means as described above and that stop supply of power when no video data is output to the external apparatus may experience the problems, as well as digital cameras.
As described above, it is an object of the present invention to provide a video output apparatus and a video display apparatus that displays video data output from the video output apparatus, which are connected using communication means that is configured to disconnect an electrical connection in accordance with the stop of the supply of power from the video output apparatus, wherein when the video output apparatus is operating in an operation mode in which after the output of video data to the video display apparatus is temporarily stopped, the output of video data is restarted, control is performed so that the electrical connection is not disconnected, thereby reducing the period of time during which no video is displayed on the video display apparatus.